1. Field of the Invention
The present invention relates to the design and operation of electrolysis cells for chemical production and more particularly to production scale electrolysis cells.
2. Description of the Related Art
High temperature electrolysis cells, such as are used for aluminum reduction are often operated using gravity stabilized liquid layers of molten metal, fused salt, etc. with the electrolysis electric current passing in a vertical direction through a shallow layer of electrolyte solution. For reactions in which gas is evolved in the form of, for example, oxygen bubbles or a deposit of a partially insulating film at an anode, the bubbles or film must be efficiently removed or the electrolyte will be displaced and cell resistance will rise.
For large industrial scale cells operating with currents of 10.sup.5 amperes and above, the magnetic field developed at the periphery of a large cell is substantial and will induce a lateral force on the electrolyte which can exceed typical buoyant forces on bubbles or low density fluids. This force can be used to displace the electrolyte toward elevated channel regions where gas bubbles may be collected. Auxiliary systems to increase this magnetic field will permit more rapid flow of electrolyte and improve cell operation.
Unfortunately in the usual geometries of circular or rectangular cells, the self-magnetic field vanishes at the geometrical center. The present inventor has been specifically involved with investigating methods for producing oxygen from lunar soil. Operation of such electrolysis cells to produce oxygen on the moon by electrolyzing molten lunar soil or rock will encounter additional difficulties in bubble removal due to lowered buoyant forces with ambient gravity (1/6 earth value) and the higher viscosities of silicate fluids. It was during these investigations that the present inventor discovered the present invention, which, although is particularly adaptable for lunar applications, has broad based general applications.
As will be disclosed below, the present invention is designed to provide a minimum total or combined field of at least 70% of the edge field.
U. S. Pat. No. 4,713,161, issued to Chaffy et al., entitled "Device for Connection Between Very High Intensity Electrolysis Cells for the Production of Aluminum Comprising a Supply Circuit and Independent Circuit for Correcting the Magnetic Field", is based on using a separate predominantly horizontal electric circuit to compensate for the self-field of a line of rectangular cells in series and also to counteract the stray magnetic field due to adjacent lines of cells. The '161 device is intended to reduce the vertical part of the magnetic field in the cell as much as possible to minimize distortion in the molten cathode pool.
U.S. Pat. No. 4,469,759, issued to W. J. Newill, entitled "Magnetic Electrolyte Destratification" and U.S. Pat. 4,565,748, issued to E. A. Dahl, entitled "Magnetically Operated Electrolyte Circulation System" discloses pumping devices which are outside the working portion of the electrolysis cell or cell stack. The magnetic field of the pumping devices disclosed in these patents have negligible penetration into the working portion of the cell or cell stack. The '748 patent uses two-phase AC excitation of the magnetic coils and induced currents in the electrolyte. The '759 device uses DC or a permanent magnetic field and imposes current flow through the electrolyte to achieve a pumping effect. Both of these devices are primarily intended for use in multi-plate batteries rather than electrochemical production cells.
U.S. Pat. No. 3,969,214, issued to M. Harris, entitled "Permanent Magnet Hydrogen Oxygen Generating Cells" discloses the use of thermal energy, only, to produce hydrogen and oxygen from aqueous acids. It uses a combination of permanent magnets and coils to produce a magnetic field substantially at right angles to the electrode faces.